The fragmentation is the problem though. One month it's a wierd bug in gcc, next month it's about how to do streaming, next month it's a game, etc.
The real problem I have with forums/boards is the completely awful interface. They don't always keep track really of what I've read or not read, I don't get notified if there's a response to my question, and so forth; and when they do that stuff they often do it in a clumsy way and every site does it differently. Then I have to remember a zillion passwords too.
I haven't had problems with the cookies getting lost on most of the forums I use. I also tend to use the same password, because really it's not like a forum account is all that important. If it does get compromised to the point I can't or won't use the account anymore, I'd just get a new account. Most forums that I frequent use vBulletin or one of the free clones (phpBB for example), so I'm pretty used to the interface. I guess all that stuff is a matter of preference.